This invention relates to analytical-sampling devices for handling analytical samples in situations wherein liquid or vapour samples contained in said devices are to be subjected to exciting radiation at the sample station of a spectrophotometer and the resulting excited radiation (also known as stimulated radiation) is to undergo spectroscopic analysis, each device being provided with a hollow imaging mirror that in use surrounds the sample, except for an optical aperture through which the exciting radiation reaches the sample and from which the excited radiation emerges, both undergoing a large number of multiple reflections within the mirror resulting in the sensitivity of said analysis being greatly enhanced. The invention also relates to spectrophotometers co-operating with said devices and to methods of spectrophotometry based on the use of said devices.
Although the present invention may find application wherever radiation stimulated in a sample by exciting radiation is to be subjected to spectrophotometric analysis, its greatest advantage is likely to be associated with its use in laser induced fluorescence and Raman spectrophotometry; this specification will make particular reference to the latter.
It is well known in the art of Raman spectroscopy that the so called Raman effect is extremely weak and that, therefore, sophisticated sampling techniques are required to optimise the collection of the desired Raman scatter and exclude as far as possible the Rayleigh scatter. Both are the result of exciting radiation impinging upon the molecules of the samples, with the important difference, however, that in the case of the former the radiation stimulated in the sample is inelastically scattered by the molecules, and, therefore, carries with it their vibrational and rotational information that permits the Raman spectrum to be traced, whereas in that of the latter it is elastically scattered and conveys no such information but only contributes unwanted background to the Raman spectrum.